The invention relates to a process for refining raw methanol and more particularly to a process for producing grade AA methanol by distilling raw methanol in several distillation stages for separating the raw methanol into grade AA methanol; tail gas and fusel oil.
Processes are known in which raw or crude methanol comprised of methanol and other components is distilled in two stages. In the first staged called a "topping stage", the components having boiling points lower than the boiling point of methanol, such as water, are separated in the second stage called a "refining stage" which consists of one or more distillation columns. However, this separation method causes a change of the concentration profile methanol/ethanol/water/pressure. In order to ensure the specified methanol quality which requires, for instance, a maximum ethanol content of 10 ppm by weight, it is necessary to provide a draw-off nozzle in the intermediate stripping section of each distillation column. The product drawn off, called "fusel oil", is a mixture of methanol, water and higher alcohols such as ethanol, propanol, etc. The fusel oil has such a high methanol content that the methanol losses, referred to the methanol content of the raw methanol produced in synthesis plants, amount to approximately 1.5% of the methanol production.